Personal emergency response systems are known in the art. Representative examples of such systems are disclosed in U.S. Pat. Nos. 4,656,319, 4,524,243, 4,064,368 and 3,989,900, owned by the assignee of the present application. The personal emergency response system includes a central station and one or more remote subscriber stations such as at a residence or business interconnected therewith.
The central station may be any facility such as a hospital, a police station, a fire station, a phone answering service or a burglary alarm monitoring service which responds to alarm messages generated by remote subscriber stations to provide assistance thereto. The central station is interconnected with the remote subscriber stations via communication links.
Various communication links may be utilized to interconnect the central station with remote subscriber stations including telephone communication lines, cable television transmission lines, radio frequency transmissions or dedicated land lines. Typically, telephone communication lines are utilized due to the prevalence of in-place telephone networks and the minimal expense necessary to interface a personal emergency response system with a telephone network.
Each remote subscriber station includes a subscriber unit interfaced with the communications link. Upon activation of the subscriber unit in response to a predetermined event, an alarm message is transmitted via the communications link to the central station.
Various means may be utilized to activate the subscriber unit to transmit an alarm message. The subscriber unit may include a timing/logic circuit which is operative to automatically activate the unit upon expiration of a predetermined period of time. A subscriber unit of this type will also include a subscriber-activated reset means which reinitializes the timing/logic circuit. The reset means may be interfaced with any device frequently used by the subscriber such as electrical switches, television sets, radios, refrigerators, stoves or telephones wherein the use of any such device causes the timing circuit to be reset to zero.
The subscriber unit may also be activated by an activator hard-wired into the subscriber unit. The wired-in activator may be part of the subscriber unit or disposed remote from the subscriber unit in one or more locations at the subscriber station.
The subscriber unit may also be activated by means of a portable activator carried by the subscriber. A portable activator is particularly useful to elderly or infirm subscribers who may be prone to acute emergencies requiring an immediate response. The portable activator also has utility for notifying the central station of an event such as a fire or an intruder in the remote subscriber station. When immediate assistance is required by the subscriber, the portable activator is manually operated to activate the system.
The portable activator is typically a wireless unit which transmits an uncoded or coded signal to activate the subscriber unit located within the remote subscriber station. Most commonly, the portable activator is a radio transmitter, although infrared and ultrasonic transmitters may also be used.
The subscriber unit of a typical personal emergency response system is a technically sophisticated device which includes a receiving unit for reception of the coded or uncoded activating signal transmitted by the portable activator, a control unit such as a microprocessor operative in response to the activating signal to implement the functions of the subscriber unit, and a transmitter subassembly activated by the control unit to transmit alarm messages to the central station. Typically, the subscriber unit includes one or more timing/logic circuits which clock one or more predetermined intervals of time and activate the control unit to perform predetermined functions upon elapse of the predetermined time intervals.
The personal emergency response system discussed in the preceding paragraphs is designed to be operative only when the subscriber is present in the remote subscriber station. Pragmatically, it makes little sense for the subscriber unit of a typical personal emergency response system to transmit an alarm message when the subscriber is absent from the remote subscriber station. Thus, those subscriber units which embody control units which automatically activate the subscriber unit to transmit an alarm message after the elapse of a predetermined duration of time must be switched off when the subscriber is absent from the remote subscriber station to preclude the automatic transmission of a "false" alarm message to the central station.
Thus, it will be appreciated that the capabilities of the system, and in particular the subscriber unit and the portable activator, are not being fully utilized. During those periods of time when the subscriber is absent from the remote subscriber station, the system is effectively inactive, and therefore not being utilized. This reduces the overall efficiency of the system.